Other ways to Validate results

Hello,

I have a database of 84 rows and 400 attributes, which is a classifier problem. I prepared the Data, that i can exercise the decission tree or other tree models. To evaluate and test the Model i use the performance operator, espacially the accuraccy. I split the Data in a ratio of 80/20. 80% is the trainingset and 20% the testset.

The result of this Model is an accuracy of 80%. When I change the Split type for example from statified to shuffled or the ratio from 80/20 to 70/30, the accuracy drops to 60%. Now my question:

Is this phenomenon normal? Is there any other way to validate a classification model? And probably a bad question which only can be answered by seeing the process: Why does the model accuracy varies so drastically by just the splitting rate or splitting type?

Thanks a lot!